1. Field
The embodiment(s) discussed herein is directed to a communications system, a communications processing method, and nodes. The embodiment(s) can be used, for example, in a case where communications is performed between the communications apparatuses (nodes) by use of the SCTP (Stream Control Transmission Protocol) or the IPSec (Security Architecture for Internet Protocol).
2. Description of the Related Art
FIG. 13 is a diagram illustrating an example of a configuration of the next generation wireless mobile communications system according to a Long Term Evolution (LTE). The system illustrated in this FIG. 13 includes, for example: more than one wireless base station (eNode B; hereinafter will be abbreviated to “eNB”), which is an entity of a wireless access network (Evolved Universal Terrestrial Radio Access Network: E-UTRAN) that a wires terminal, as an example of a user equipment (UE), accesses through a wireless link; and an MME (Mobility Management Entity)/S-GW (Serving-Gateway), which is a superordinate apparatus of the wireless base stations.
In such a system, communications between the eNB and the MME/S-GW is performed through an inter-apparatus (entity) interface called an “S1 interface”, and communications between the eNBs is performed through an inter-apparatus (entity) interface called an “X2 interface”.
Here, the S1 interface connects the eNB, which is a network entity of the wireless mobile communications system, with the MME/S-GW apparatus, which is a superordinate apparatus of the eNB, by use of IP (Internet Protocol), and is used for transmitting a control plane (C-Plane) signal and/or a user plane (U-plane) signal.
The X2 interface is used for connecting the eNBs each other by use of IP to transmit a control plane and/or a user plane signal. As depicted in FIG. 14, when a UE moves from a certain eNB wireless zone (cell or sector) to another targeted eNB wireless zone and then performs handover (HO), in which the connection destination is switched into the targeted eNB, the X2 interface can be used to transmit packet data (hereinafter, will also be simply called a “packet”) sent from the MME/S-GW to the HO source eNB of the UE (see the dashed-dotted line). In this instance, the following non-patent document 3, for example, describes such HO processing.
In such an interface as the Si interface and the X2 interface, one of the protocols used for transmitting an inter-apparatus (inter-node) control signal is called the SCTP (Stream Control Transmission Protocol).
The SCTP means verifies the correctness of a packet on the IP based on sequence number and check sum, and is one of the protocols in the transport layer which enables information transmission while avoiding redundant packet transmission, packet loss, or the like, as far as possible, thereby ensuring reliability. For example, the SCTP is regulated by the following non-patent document 1 (RFC4960).
The network entity (hereinafter, will be also called the “node”) provided with an SCTP function has one or more than one logical terminal point called an “endpoint”, and establishes a logical connection (SCTP link) called an association with the endpoint of another node. At that time, the node (endpoint) has two states as a client and a server. A client is required to operate as the sender end of a node connection (association) establishment request; a server is required to operate as the receiver end of the connection establishment request.
A packet under the SCTP includes an SCTP common header and one or more than one data block called a “chunk” subsequent to the common header. The chunk can be divided into two types: a control chunk storing a control signal (message) therein; and a data chunk storing user data therein. The control chunk is sent out at the time of establishment (initialization: INIT) and release of an association.
For example, at the time of association establishment, an INIT chunk, an INIT-ACK chunk, a COOKIE-ECHO chunk, a COOKIE-ACK chunk, and so on, are used as a control chunk. On the other hand, at the time of association releasing, a SHUTDOWN chunk, a SHUTDOWN-ACK chunk, a SHUTDOWN-COMPLETE chunk, and so on, are used as a control chunk.
FIG. 15 is a diagram depicting an example of a format of an SCTP packet. As illustrated in FIG. 15, the SCTP packet has a common header and one or more than one chunk (control or user chunk) subsequent to the common header. The common header includes a sender source port (Source Port) field (16 bits), a destination port (Destination Port) field (16 bits), a verification tag (Verification Tag) field (32 bits), and a checksum field (32 bits).
In the common header, the port number of the transmission source endpoint is set to the transmission source port field, and the port number of the destination endpoint is set to the destination port field. With such port numbers, associations are identified. To the verification tab field, key information for preventing arrival of an old SCTP packet (identifying the currently effective association) from the prior association is set.
To the checksum field, the checksum of an SCTP packet for ensuring the completeness of data [detecting a broken packet (transmission error)] when the SCTP packet is transmitted through an IP network.
In the chunk subsequent to the common header, the type and the length of that chunk are indicated using the leading 32 bits, and user data or control data is stored thereafter. In this instance, FIG. 15 illustrates an example of a format of an SCTP packet in which N-number of user chunks are set subsequently to the common header, a single SCTP packet being thereby set.
Next, FIG. 16 depicts an example of a format of an initialization (INIT) chunk, which is a control chunk used for association establishment. FIG. 17 depicts an example of a format of an initialization response (INIT-ACK) chunk, which is a response to the above mentioned control chunk (initialization chunk).
As depicted in FIG. 16, the INIT chunk, which means a request for association establishment, is indicated to be an INIT chunk when the chunk type (Type)=1, and the initialization value of the information necessary for association establishment is set thereto.
In contrast, as illustrated in FIG. 17, the INIT-ACK chunk is indicated to be an INIT-ACK chunk when the chunk type=2, and the endpoint (server) that has received the INIT chunk is added with information (cookie) or the like identifying the association establishment request generated based on the reception information. According to the SCTP, the use of a cookie makes it possible to avoid impacts (shortage of system resources or the like) of Dos (Denial of Service) attacks.
FIG. 18 depicts an example of a handshaking (4-way handshaking) sequence at the time of SCTP association establishment in the SCTP. In the beginning, the client-side endpoint sends an INIT chunk to the server-side endpoint for association establishment.
Upon reception of the INIT chunk, the server-side endpoint sends an INIT-ACK chunk containing a cookie to the client-side endpoint.
Upon reception of the INIT-ACK chunk, the client-side endpoint extracts the cookie and sends the extracted cookie, in the form of being contained in a COOKIE-ECHO chunk, to the server-side endpoint.
Upon reception of the COOKIE-ECHO chunk, the server-side endpoint extracts the cookie and then sends a COOKIE-ACK chunk.
In the above described manner, an association between the client and the server is established.
FIG. 19 is a diagram illustrating an example of a protocol stack of the control plane of the Si interface in the LTE; FIG. 20 is a diagram illustrating an example of a protocol stack of the control plane of the X2 interface in the LTE. In this instance, these are described in, for example, the following non-patent document 2.
As illustrated in FIG. 19, according to the S1 interface, the protocol stack of the control plane is regulated as the physical layer, the data link layer, the IP layer, the SCTP layer, the S1-AP (application) layer, in order, from the lower layer. On the other hand, according to the X2 interface, as illustrated in FIG. 20, the protocol stack of the control plane is regulated as the physical layer, the data link layer, the IP layer, the SCTP layer, the X2-AP (application) layer, in order, from the lower layer. Here, the Si interface and the X2 interface differ from each other in operation of association establishment that the entities (eNB and MME/S-GW) employ.
In the section of the S1 interface, as indicated in FIG. 21(A), for example, the eNB and the MME/S-GW operate as a client and a server, respectively, and the SCTP association, as described above, is established (handshaking).
In contrast, in the section of the X2 interface, as indicated in FIG. 21(B), for example, the eNB is required to be capable of operating both as a client and a server and to realize handshaking with the opposite eNB.
[Non-patent Document 1] RFC4960 (IETF Network Working Group)
[Non-patent Document 2] 3GPP TS36.300 V8.3.0; Chapter 20.2
[Non-patent Document 3] 3GPP TS36.423 V8.0.0; Chapter 9.1
As described above, in a case where an SCTP association is established between the eNBs for realizing communications between the eNBs through the X2 interface, the eNBs can operate both as a client, which is a transmission source of a connection establishment request (INIT chunk), and a server, which sends back a response (INIT-ACK chunk) upon reception of the request. Therefore, the opposite two eNBs are capable of mutually operating as clients.
In this case, as illustrated in FIG. 22, when the different eNBs each having more than one LAN (Local Area Network) port sends a connection establishment request (INIT chunk) to the opposite eNB, both operating as clients, there is a possibility that two or more (redundant) associations are established between the eNBs.
That is, as illustrated in (1) of FIG. 22, it is assumed here that, one eNB#1, which operates as a client, uses transport address a (IP address=192.168.0.1; port number=100) to send a connection establishment request (INIT chunk) toward transport address c (IP address=192.168.0.3; port number=200) indicating the destination endpoint.
At that time, if the opposite eNB#2 also uses transport address d (IP address=192.168.0.4; port number=200) indicating the transmission source endpoint to send a connection establishment request (INIT chunk) to transport address b (IP address=192.168.0.2; port number=100), two or more associations (A and B) are established between the eNB#1 and the eNB#2 as illustrated in (2) of FIG. 22.
Such a case may occur in, for example, the already described HO processing. That is, it may occur after the UE moves from the wireless zone of the first eNB to that of another (the second) eNB, or in a case where the UE or another UE moves from the wireless zone of the second eNB to that of the first eNB.
However, it maybe impossible for a communications application (a protocol of the application layer) used in inter-node communications such as HO processing to identify (specify) the eNB from SCTP information belonging to the transport layer lower than the application layer or IP information belonging to the network layer lower than the transport layer.
That is, it is possible to obtain the parameters that regulates the port numbers of the opposite eNB and its associations from the SCTP shared header information indicated in FIG. 15 and information (parameters) contained in the INIT chunk and the INIT-ACK chunk depicted in FIG. 16 and FIG. 17, and it is also possible to obtain the IP address from the IP belonging to the layer (network layer) lower than the transport layer which the SCTP belongs to. However, since such parameters are incapable of expressing with which one of the eNBs an association has been established, it is impossible for either of the eNB#1 and the eNB#2 to recognize that more than one association has been established between the nodes.
In this manner, when more than one association is established between the eNBs, association management more than need to be is required, so that an increase in memory amount to be allocated to association management in the eNB results in running out of apparatus resources, and that the processing amount such as a heartbeat keep-alive mechanism due to heartbeat generated per association is increased. These may cause deterioration of the performance of the eNBs.
In this instance, the heartbeat keep-alive mechanism means processing for evaluating whether or not an unused destination address is active by means of periodically sending a heartbeat packet to the address that has not been used for data transmission for a certain time period.